Development of less-expensive and high performance power electronic devices is essential to support commercialization of new technologies from integrating energy harvesting and storage devices to electric vehicles to solid state lighting to high power microelectronics. One of major technical barriers is the ability of materials and components for efficient thermal management. Thermal interface materials (TIMs) play an important role in enabling a wide range of power electronics because TIMs account for over 50% of the heat dissipation in most high power devices. Low thermal resistance TIMs that can work reliably at higher temperatures will greatly improve the performance and lifetime of power electronic. Conventional TIMs have performance and practical limitations in power electronics because of low thermal and electrical performance or poor thermo-mechanical reliability, or both. Current state-of-the-art TIMs using metals such as indium and its alloys can work up to 150° C., but they are fairly expensive, while raising their own reliability concerns.
Power dissipation in electronic devices is projected to increase significantly over the next ten years to 150 W/cm2 and beyond for high performance applications (1). This increase in power represents a major challenge to systems integration since the maximum device temperature needs to be around 100° C. or higher. Typical thermal interface materials (TIMs) used in production today include thermal greases and adhesives, thermal gels, phase change materials, and low melt point solders such as indium (2). The thermal conductivity for these materials ranges from about 3 W/mK (grease and adhesives) to 50 W/mK (solders), which is not sufficient to meet the high-end demands in future electronics needs. Recently, high power LED lighting products have enjoyed rapid growth, renewing the need for thermal management solutions with right performance/cost tags. A higher junction temperature in LED chip reduces both the luminescence efficiency and the life span of LEDs, adding to the cost and threatening the viability of the technology (3). Development of suitable TIMs is important to support and facilitate the large LED lighting market. The key challenges in designing TIMs include material properties (matrix and filler of TIM pastes), interfacial resistances, and the assembly processes to achieve desirable thickness, composition, and bond strength.
Carbon nanotubes (CNTs) are promising new materials exhibiting extraordinary thermal properties to address thermal management challenge (4-6). Recent studies on both random CNT composites (7-9) and aligned CNT arrays (10-14) have shown less than ideal characteristics. There are significant challenges which include reducing structural defects in CNTs and lowering thermal resistance at filler/matrix and TIM/solids interfaces. Various approaches to address those issues using hybrid nanomaterials and interfacial engineering have been proposed (15).
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